An anchor is a device used to attach a floating vessel to the water bottom or a fixed object on the water bottom for the purpose of holding the vessel in place. Anchors are connected to the vessel by ropes, cables or chains. Primitive anchors were heavy and relied on enormous weight and friction along underwater surfaces to hold a vessel. The structure of many modem anchors enables them to actually dig into the underwater surface and grip the sea, lake or riverbed powerfully against the drift of the vessel. The common anchor consists of a shaft, with a movable crosspiece called the stock at its top end, and at its bottom, two curved arms ending in spade-like points, called flukes. These common anchor designs are excellent for anchoring a vessel to a sandy or muddy bottom; however, they do not work very well when the bottom is a hard structure such as a wrecked ship or a corral reef. First, there is nothing for the spade-like flukes to dig into and second the anchor often gets tangled in the structure. When this latter situation occurs, the anchor often has to be cut loose, the line breaks, or a cleat is torn off causing damage to the boat in efforts to free the anchor. Also, if the anchor can be pulled free the underwater structure is often damaged. These common anchors are relatively expensive so the loss of an anchor can be a significant loss.
A grapnel is a relatively small anchor usually with four or five flukes and is used for grappling on to an underwater structure for the purpose of securing a vessel. These anchors work well at securing a vessel to an underwater structure such as a ship wreck or a corral reef, but often they also cannot be freed up when it is time to move on and as a result many are lost. Much damage can be done to a reef or boat in the course of freeing them from the structures when this is possible.
What is needed is an anchor for anchoring a vessel to an underwater structure which can be easily freed up and freed up without damage to the structure.